"Crystal-people like lots of people. I like you and you can join us. I also know you have a project, so if you want to leave that is also good. Or if green man doesn't want more people," she says.

She'll come, then.

He offers her a hand across the threshold, and then turns back and finds himself confused about what the equivalent should be for Weeping Cherry.

Weeping Cherry briefly considers hopping over the boundary such that she taps his foot at the same time as touching the floor, but decides to play it safe.

"Crystal-people don't need to be invited to be comfy. But also I don't want to make you uncomfy by coming in without you saying," she explains. "I can come in?"

Sure, that works. He assumes someone has explained to her how ownership claims work and that she shouldn't touch anything marked as belonging to someone, but just to be on the safe side he'd like to confirm that; it's important not to mess with the machinery while it's in use.

"Yes! I will not touch anything. I will look and listen," she confirms. She hops over the territory boundary and then follows in her normal sliding fashion.

After a moment, she wonders whether backscatter x-rays would be a problem.

"Can I shine a transparent light on the machines? Or would that hurt them?" she asks.

What kind of transparent light? Some of that kind of thing is dangerous to Crafters, even if it's fine for the machine. (He thinks it's probably fine for the machine, but he'd rather check on some spare parts, once he's sure it's safe for him.)

"I don't have the words. Too much is bad for crystal-people without crystals, but I can shine very carefully."

She makes a little laser pointer wander around the floor to demonstrate.

"I would shine a small amount. Each shine would be the amount of this kind of light you get by standing on a tall mountain for one minute," she explains. "But if you say no, I won't. I am curious about the machines, but I don't want to hurt anyone."

That will definitely be fine, then, plenty of the machinery is outside and it's hardened enough to be there indefinitely.

Does she have any other questions?

She does! She bets she has enough questions to last the walk until they get there.

"How similar do parts need to be in the machine?" she asks. She shows a foot-long ruler on the floor. "The marbles are one in 120 of this similar? One in 12,000? How do you know if parts are similar enough?"

The marbles are copies of each other, so they're entirely identical! There are different kinds that make different sounds, and they're marked to show that so the Crafters can figure out what's happening if there's a problem, but the different sorts were originally copied from the same example without any other modification, so all their other traits are the same. The rails are mostly identical too, but as long as the marbles will go through them reliably and at the right speed, it doesn't matter very much. The engineer usually adjusts the speed by adjusting the rails' friction, and includes a leveling-bubble tube so they can make sure they have the slopes right when they install them.

Oh, that makes sense. And obviates some of her other questions about the construction, if they can just vary the friction appropriately.

"How many kinds of marble are there? When one part of the machine gives several marbles to another part of the machine, does it give them one after the other, or on different rails?" she asks.

There are eight kinds of number marbles - there could have been any number, but there's some math he can recommend a book about if she wants about what tones sound nice together, and eight is an important number for that, and the Crafter who invented the library decided to do it based on that - and four special marbles that mark the beginning and end of a book request and separate the part of the request that specifies the book from the part of the request that specifies where it's going, in one direction, and separate the instructions for each glyph, in the other. Most of the special marbles were added later, when the library went from being just one person's thing to sending books everywhere via ansible. All the marbles for a given request go down the rails together, but there's a system to send different requests down different rails in parallel to let the machine work faster without getting jammed up.

Interesting! She supposes that without needing to base things on binary like a digital computer or trinary like some early mechanical computers, you're free to choose any base. She wonders how the ideal choice of base interacts with radix economy.

"How big is the whole machine?" she asks. "How long of rails, doing how many things at the same time?"

They don't keep very close track of the total length of the rails, but it's somewhere in the tens of thousands of kilometers; they currently have between 17,300 and 17,400 user ansibles connected to the machine and can read requests in from about 5,000 and send books out to nearly 2,000 of those at once.

Wow! That's incredible. Her world never produced such large mechanical computers, albeit because they switched to digital.

"How do you send a request to the right part?" she asks. She's beginning to think she should have consulted some of their local computer science books before asking for a tour, but she's still excited to see it first-hand.

There's a lot of steps to that! It starts when the user sends in the code they want; that's read off the ansible and translated by the machinery into a series of marbles. Those then go into a machine with a section of track that can tilt down, and marbles denoting zero are added to the top until it's full; every time they get to the point where the longest book code is another digit longer they have to change that bit to make room for the new digit. Then the special marbles denoting the beginning and end of that section are added, and the marbles that encode where the ansible is, so the machine can find it again when it has the book. The marbles then go off to a reader, which checks the first marble to make sure it's makes the 'beginning' tone, and then it checks the second marble to see what tone it makes and adjusts the track depending on what it hears. Once it's checked the second marble, it removes it, so when the request gets to the next reader the old third marble is the new second marble, and that gets checked and removed. Once it gets to the last marble in the code, it's made its way to the book that was requested, and from there the track is made in a way that lets the encoded book follow along behind the marbles in the second part of the code, which lead it to the reader with the ansible in it in the same way the marbles were led to the book in the first place. Then once they get to the reader, the encoded book goes into that and the reader decodes it into a series of marbles that are then translated into ansible nudges to send back to the person who requested the book. Of course that's a simplification; there are extra bits of machinery that do things like sending the entire request to a holding lane if there aren't any readers free or the book it's looking for is already being read by someone else, or that handle things like the library having a few copies of a very popular book available or something going wrong with how the request is put together. It gets really complicated!

She starts idly tracing out what the schematic of that would look like in her notes.

"I see. Why read the disk into marbles, and then the marbles into the ansible? Why not the disk into the ansible?" she asks.

Well, the machinery sections that read the book and manipulate the ansible are fairly bulky, so they'd need some kind of machinery to move data between them, and marbles are as good as anything else they could use for it. In general there's never just one way to do any particular part of a given machine, but if you do things too many different ways it makes the whole thing harder to understand and work with. The library's machinery is already too big for any one person to really understand, they don't want to make it any more fragile that way than they have to.

Yeah, with so many concurrent things happening, robustness is probably very important in the design. She expects that does terrible things to their transfer rate, though. If the disks were read off directly by the ansible, they could read vibrations off much faster than it's practical to release marbles.

"What part of the machine do you work on?" she asks, because probably she can ask more questions about the complexity/speed tradeoff once she's seen the actual machine parts they're working with.

His territory is mostly routing, but he's got the main holding area for when they have too many requests and need to make some of them wait, and some book storage, including some popular ones with duplicates in storage if she wants to see how that's handled; he doesn't have any of the machines for actually reading a book out into an ansible but he has a good view of one over on the north side if seeing it from a little distance will do, otherwise she'll have to wait for someone with one to to agree to let her in for a tour, which might be a few days. And then the ansible and marble storage is mostly upslope, he can't help her with that today.

Routing sounds like a pretty challenging part of the whole thing, yeah. She wants to see at least one disk, because she wants to try decoding the book directly off of it. If she can, maybe she can get herself installed in the machinery in such a way as to be able to read books directly.

"That sounds good! A far look is good," she reassures him. "Why do you work on machine parts and not on writing disks or designing machine parts?"

Well, in some ways his job is the easiest one in the whole place, right; he does need to know how everything works, but he doesn't need to figure anything out about how it should be, that's up to the engineers and programmers. And he doesn't have to meet with people when he doesn't want to; he'd go nuts living as close with other Crafters as the formatting team does, or spending as much time talking to them in person as the programmers do.

That makes sense to her. Maintenance does sound like a good job for someone who wants to be alone with machines.

"I see! It seems like good work for you. Why do you work on book project at all?" she asks. "Not working on it would be easier."

He in particular grew up here, his father is one of the other maintenance techs! He moved away for his first territory, but he missed it, so he came back when they had a territory available. Most of the other maintenance people just really like computers but aren't interested in designing their own for whatever reason.